OK, there's two 30 amp circuits, two 5 amp circuits, a 15 amp shower and a spare. I want to put a 32 amp cooker on the spare. clearly the load isn't just all those added together. Anybody know somewhere I can find typical figures for the load from the house or suggest an answer?
I have:- fridge, freezer TV, PC, usual number of lights. shower, 2 small heaters upstairs, elec blanket.
(no immersion).
the heaters would be 1KW or less , so that's 1000 / 240 = (about)
4 amps for each heater if my schoolboy physics is still functioning.
shower on 15 amp fuse cant be more than 12 two heaters + blanket 12? cooker 28?
that could be 52 without all the little things if everything was running at once?
You'll find _an_ answer in Table 1B of the IEE On-Site Guide (OSG). (But apply that to a lot of house installations an you'll come up with an ADMD (after diversity max. demand) of 150 - 200 A! So some common sense has to be applied too.
Anyway, using Table 1B, in your case:
- two 30 A circuits - socket rings, presumably; allowance is 100% of first cct. + 40% of others - so 42 A (this really is over-generous, IMHO);
- two 5A circuits - lights; allow 66% of actual max. load, let's say 6 A (assuming 2 kW of lighting);
- 15 A shower? - perhaps you meant immersion heater - anyway assume 3 kW or 13A (no diversity allowed for water heating);
- total so far, 61 A;
- add cooker: assume typical free-standing cooker - about 12 kW flat-out (52 A, diversity rule is first 10A plus 30% of remainder, giving 23 A - new total 84 A.
So applying the OSG strictly you'd need to upgrade to a 100 A supply. In practice you won't have any problem and (IME) the electricity companies don't worry over-much about this sort of thing. Anyway 84 A is only a small overload and will do no harm for short periods (it certainly won't blow your main fuse).
Oh, no immersion. So what's the 15 A fuse feeding - an old 3 kW instant electric shower? (and people think the 9 kW ones are poor) - or a shower pump (with gas or oil water heating)? If it's a shower pump you can reduce the 13 A I assumed above to one or two amps.
If that is an old 3 kW shower and you ever upgrade it to a modern one, that would be the time to get your supply uprated.
It depends what you mean by "shower". An electric shower is usually 32-45A. Perhaps you mean a shower pump on its own circuit?
Personally, 60A would be fine, provided you have only one of an electric cooker and electric shower. If you have both, then I'd be tempted to get them to stick a 100A cutout on it. If you have mainly electric heating, then you should be aiming for 3 phase.
yes! (something to note if I upgrade shower, never realised they are 9 now!!! ) And thanks for the rest of the info.
Two more questions (I'm still vacillating between DIY and getting a new fusebox fitted)
What is the view on a ring main junction box for a spur mounted on the wall near the fusebox rather than under the floor (i need to free up the fuse the freezer is using) I really don't fancy ripping up the floor to add a spur, alternatively I could utilise the (repositioned) 13A supply to the old gas cooker with a long cable, bit naff. but it would work.
Fuse holders. My Wylex fusebox has fuse-wire fuses (25 years old) I tried to get a green coloured one for the cooker position (perfectionist, me :-)) , the one I bought in a DIY shed turns out to not fit Do people reckon I'll find one that fits in a better shop?
Thanks again for all the help, I shall stay subscribed here (who groaned at the back?) , bloody good group, hopefully I will be able contribute something.
Old 3K unit it seems, I didnt realize how puny it was by modern standards!
The cooker will have two e. ovens (but there is only puny-shower) and gas hobs (and a gas oven) wife has chosen a pretty fancy cooker. (but 30A not 45A).
I'd say 60A would work fine as it is then. However, enquire about a 100A cutout, explaining that you have an electric cooker and shower. They might pop round and upgrade you for free.
However, your consumer unit is old and relatively dangerous (wire fuses are much worse than cartridge fuses or MCBs). I'd would strongly advise replacement.
more I think about it, less I like the idea of something unconventional, like that. Using the 13A cooker point is a more conventional solution and with wiring, unconventional may be a danger to those who come after. An extension cable goes with me and poses no risk of confusion to others. Its going to be easier than breaking into the ring anyway.
The highest powered ones are about 10.8 kW (needs 10 mm^2 cable).
Either of those positions would be OK, but why not just wire the spur into the fuse box? There's nothing to stop you taking a spur from the origin of the circuit, in fact it's a better way.
Green is 45 A and won't fit the older Wylex boxes, as you've just discovered. 30 A (red) one should be OK for your cooker circuit. If you really need a 45 A circuit you'll have to get a separate 1-way Wylex box and split the meter tails using service connector block (Henley block).
Individual domestic cooker circuits don't have to be rated for the full appliance load, as the probability of having all the rings and things on at once is tantamount to zero. You're allowed to use the same diversity rule that I mentioned before - so if it's a 12 kW cooker the circuit design current is 23 A and a 30 A fuse is quite OK. 6 mm^2 cable is usual, but check the grouping and other derating factors to be sure.
Right, why didnt I think of that? There's an example in the existing wiring too (done by me with guidance 25 years ago). I seem to be having a "senior day" with this job. Still, better to ask stupid questions than screw up.
Right, I'm the victim of procrastination here, I was going to do a 45Amp set up, (to future proof) and bought 45A, then changed my mind in face of the load issue. I'll get a 30 tomorrow.:-S
I was going to say the hobs gas anyway, but that's not the point is it. Someone after me could do otherwise. Or even me in 5 years time with my memory!
thanks again, (I have that cable). I reckon if I lurk in this group I will be a lot better informed after a while!
Anyway I don't agree with Christian - a 25 year old Wylex fusebox is likely to be perfectly safe, assuming there's been no abuse like fitting "uprated" fuse-wire.
It's old rubber-cable installations you have to watch, and really old fuseboxes which have fuses in the neutral as well as the phase.
Quite frankly, I wouldn't be surprised if replacing the fuse wire with a nail was actually safer!
Cartridge fuses are another matter. They are perfectly safe and the only reason to change one of those for a modern unit is for convenience, or if earth leakage protection is required and it is the simplest method to achieve this.
In some circumstances I'd prefer a fuse to an MCB. The rewirable ones are perfectly ok in Wylex boards as long as the holder is intact and has the correct size wire.
A 25 year old wylex can probably be upgraded to plugin MCBs quite easily. They are available in the sheds and (cheaper) from TLC, and replace the existing fuse and holder. The cover will require the knockouts removing as well.
Many times and whilst a bit spectacular on the flash/bang front not anything to be overly concerned about. Its not so many years since rewireable fuses were the norm throughout the country. "REPEATED" rewireable fuses blowing could however leave deposits of condensed copper on the (usually Asbestos) target area and this has been known to carry more current than the fusewire if not cleaned off or the target/enclosure replaced
Stop eggaggerating, you will be sounding like dimm if you carry on.
The old Wylex boxes could be fitted with cartridge fuseholders or plug in MCBs. However the fact remains Rewireable fuses are still acceptable.
I'm probably more cautious because I've seen a fire started by a rewireable fuse, when it lit all the fluff that had accumulated on the consumer unit. It was only luck that this fire didn't actually spread, although the scorch marks were quite impressive.
Although still allowed by the regs, I would still replace any rewireable fuse holder in any house in which I had some sort of interest in the safety of. Even if not replacing the consumer unit, it's not expensive or difficult to replace them with cartridge fuse holders or circuit breakers.
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